Natural circulation systems offer simplicity, enhanced safety and reliability and thus are advantageous over their forced cir­culation counterpart. However, natural circulation is suscepti­ble to flow instabilities. These instabilities are undesirable for various reasons. Literature suggests the use of orifices at the in­let to suppress instability. However, orificing introduces pres­sure drop which limits the flow rate and hence the heat carry­ing capacity of the fluid. In the present study, investigations have been carried out with different mechanical gadgets to con­trol the natural circulation flow instabilities. Extensive experi­ments have been carried out in a single-phase rectangular nat­ural circulation loop to study the effect of these mechanical gadgets on instability. The paper brings out the results of ex­perimental investigations carried out on the role of mechanical gadgets in controlling instability.